Regenerative air heater such as hot blast stove

ABSTRACT

The blast stove comprises a preferably cylindrical hollow vertical body of refractory bricks closed at the top by a dome of refractory bricks overlying and protruding radially outside the vertical body at the top thereof, the entire body and dome is surrounded by a jacket of steel, and the dome is built up on and is supported by a steel annular element which is in a gas-tight manner connected to the outer steel jacket of the dome and of the vertical cylindrical body, the connection of the said annular element to the steel jacket of the vertical body and/or of the dome extending with respect to the axis of the vertical body alternately in a mainly radial and in mainly axial directions, this annular element being supported by a row of brackets secured to the outer jacket of the vertical body at a larger distance downwards from the upper edge of the vertical body than where the connection of the annular element to the vertical body is positioned, and preferably at at least twice the last mentioned distance. Several species and auxiliary features are also disclosed.

United States Patent Van Herk et al.

[ REGENERATIVE AIR HEATER SUCH AS HOT BLAST STOVE Inventors: CorneliaVan Her-k, l-laarlem; Johannes Cornelk Mes, Alkmaar, both of NetherlandsKoninklflke Nederlandsche lloogovens Ent. Staaltahriken N.V.

Assignee:

Filed: March a, 1971 Appl. No.: 121,762

[30] Foreign Application Priority Data US. Cl. ..263Il9 R Int. Cl...F23l 15/00, F23m 9/00 Field of Search ..263/l9; 266/l4 ReferencesCited UNITED STATES PATENTS 10/1939 Linder ..263/l9 R 3/1966 Pentek..263/l9 R 8/1967 Nisaida et al. ..263/l9 R 1 51 Sept. 12,1972

Primary ExaminerEdward G. Favors Attorney-Hall & l-Ioughton 57] ABSTRACTThe blast stove comprises a preferably cylindrical hollow vertical bodyof refractory bricks closed at the top by a dome of refractory bricksoverlying and protruding radially outside the vertical body at the topthereof, the entire body and dome is surrounded by a jacket of steel,and the dome is built up on and is supported by a steel annular elementwhich is in a gastight manner connected to the outer steel jacket of thedome and of the vertical cylindrical body, the connection of the saidannular element to the steel jacket of the vertical body and/or of thedome extending with respect to the axis of the vertical body alternatelyin a mainly radial and in mainly axial directions, this annular elementbeing supported by a row of brackets secured to the outer jacket of thevertical body at a larger distance downwards from the upper edge of thevertical body than where the connection of the annular element to thevertical body is positioned, and preferably at at least twice the lastmentioned distance. Several species and auxiliary features are alsodisclosed.

REGENERA'I'IVE AIR HEATER SUCH AS HOT BLAST STOVE This invention relatesto a regenerative air heater, in particular to hot blast stoves for usewith blast furnaces, comprising a preferably cylindrical hollow verticalbody of refractory bricks closed at the top by a dome of refractorybricks overlying and protruding radially outside said vertical body atthe top thereof, the entire structure being surrounded by a jacket ofsteel of the vertical body and of the dome.

when building air preheaters the development at present is into thedirection of ever increasing sizes thereof and the structure shouldmoreover sufl'lce ever increasing requirements of thermal load. Thisgives rise to structural problems as a result of the occurence ofconsiderable difierences in thermal expansions and contractions ofseveral parts of the structure. Said differences in thermal dilatationsetc. cannotbe entirely taken up by the normal distributionof s in thestructure and thus they often give rise to the occurrence of cracks inthe refractory lining of the vertical body and ofthe dome. v

A particularly vulnerable. area in this respect is the zone where thedome merges into the vertical body. By the choice of a structureas givenabove and which is known as such, having a dome which protrudes radiallyoutside the vertical body it is possible to solve such difficulties to aconsiderable extent. This is particularly true for an earlierimprovement suggested by the applicant in which the lower edge of thedome is formed by a row of pivoting columns supporting the dome.

However, such structures introduce another structural difficulty. Theprotruding dome should be supported by a supporting structure positionedaround the vertical body, which structure should moreover be part of thegastight outer jacket of the structure. Up to now it has not appearedpossible to find a structure forthis support which not only gives a goodgastight outer jacket, but which also gives a good supporting of thedome without inadmissible occurring in this part of the steel outerjacket. Such stresses are caused by the fact that the upper edge of thevertical body, to which the supporting structure is secured, is hot,whereas the lower edge of the protruding dome is of lower temperature.This lower edge and the part of the supporting structure upon which itrests, will thus expand in a radial direction to a much lesser extentthan the upper edge of the vertical cylindrical body. The situation asto the loads in structure caused thereby in this area will not only giverise to the damaging of the steel structure and thus to leakage of theair heater, but also to the occurence of cracks in the refractory innerlining of the air heater supported by said steel outer jacket.

in view of the above the invention has for its purpose to remove theobjections as given above by providing a novel and very simple structureof the air heater. in view thereof the present invention consists inthat in an air heater as given in the preamble the dome is built u onand is supported by a steel annular element which IS in a gastightmanner connected to the outer steel jacket of the dome and of thevertical cylindrical body, the connection of the said annular element tothe steel jacket of the vertical body and/or of the dome extending withrespect to the axis of the vertical body altemately in a mainly radialand in mainly axial directions and that this annular element issupported by a row of brackets secured to the outer jacket of thevertical body at a larger distance downwards from the upper edge of thevertical body than where the connection of the annular element to thevertical body is positioned, and preferably at at least twice thelastrnen' tioned distance.

Withtheaidofthissmictureitisobtainedthatthe relatively cold lower edgeof the dome is supported by brackets cormected to the outer jacket ofthe vertical body in a zone which does not differ very much intemperature from this lower edge and only differs therefrom to anextent, which does not give difficulties and which is deemed admissible.The elements exerting the function of summing the dome thus are loadedonly slightly and to an admissible extent by thermal s. The t sealingofthe dome and the vertical body thus has an elastic nature and shape,so that this is neither loaded inadmissibly by the occurence ofdifi'erences in thermal deformation between the upperedgeofsaidbodyandthesupportofthedome. 7

In fact the new structure to the invention thus gives a situation inwhich the function of sealing against the outflow of gases and thefunction of supporting are separated in an efficient manner, so that allelements of the structure functioning for supporting the dome arerelatively cold, the elements serving for'the sealing against theoutflow of gases having elastic deformation properties.

It is therewith not necessary that the annular element, onto which thedome is built up, has almost the same temperature as the brackets and asthe part of the outer jacket of the vertical body to which they areconnected. This is particularly so because it is quite well imaginableto position the annular element on the brackets in a manner so as to befreely slidable, if desired with a system of sliding blocks between theannular element and the brackets, or longitudinal bearings (linearhearings) or the like."

Structurally such an embodiment is, however, not very attractive as itrequires a large number of mutually separate structural elements.Moreover such a solution will entrain the requirement that the annularelement, the upper surfaces of the brackets and, if present, the slidingblocks or the like, should be assembled in a manner which gives theutmost accuracy as to their mutual positions in order to obtain auniform supporting of the annular element.

Thus an embodiment according to the invention is preferred in which theannular element is rigidly connected to the brackets.

In order to avoid connecting problems between the outer jacket of thedome and the annular element as a result of the occurence of thermalstresses, it is possible to couple these two structural parts also by aconnecting member having a shape so as to be elastic. However, inpractice this has not appeared necessary and even such a structure couldentrain disadvantages as a result of a too easy possibility of movementbetween the refractory brick part of the dome and the outer metal jacketthereof.

Thus it is preferred according to the invention to embody such an airheater in such a way that the annular element is immediately, rigidlyconnected to the outer jacket of the dome, so without intermediaryparts, but

is connected to the outer jacket of the vertical body by a connectingpart which extends alternately in different directions.

Depending upon the question whether this connecting part has more andlonger axially extending parts, the elastic deforrnability thereof willincrease and thus the thermal deformations of the upper edge of thevertical body with respect to the dome will better be taken up. Anopposite consideration is, however, that a considerably profiledconnecting part takes up more space and thus requires a more pronouncedradial protrusion of the dome over the vertical body.

Moreover, such a connecting part entrains a more expensive structure.Thus according to the invention it is preferred to apply an embodimentof the invention in which the connecting part only has three curvedparts, in total taking up an angle of 200 to 350. This boils down to thepresence of only a single or a few axially extending parts in theconnecting part. It has appeared that this gives the possibility ofelastic deformation to an extent which is sufficient in practice. Ausual structure detail of the brackets, which could also be applied inthe proposed structure, in such that the dome with the lower edge restsupon a plane horizontal part of the brackets. Often the shape of thedome in the proximity of the lower edge is also almost cylindrical.Thanks to this new structure of the air heater it has, however, appearedpossible to give the dome a shape which has less curvature, the annularelement according to the invention having the shape of a frustoconicalbody, the lower edge of the dome being perpendicular to this conicalsurface in the zone where it is supported thereby.

The danger that the dome may slide in the transverse direction withrespect to the vertical body is considerably restricted by this feature.In order to avoid also that parts of the dome will slide in a radialdirection with respect to other parts thereof it is further preferableto provide the annular element with means for arresting the position ofthe lower edge of the dome. In particular such means are recommended ifthe dome along the lower edge consists of pivoting parts according to anearlier proposal by the applicant as indicated above.

A further simplification consists in that the brackets are provided withat least one reinforcing flange at the outside, this flange mergingfluently and gradually into the outer lining of the dome. In practicethis will be embodied so that these flanges will be part of the steelsheet jacket which forms the outer lining of the dome.

The space between the lower edge of the dome and the upper edge of thevertical body is positioned outside the flow of hot gases through theair heater. This gas quantity present in this zone will give a heatinsulating effect between these two elements and thus will also protectthe steel connecting part somewhat against too high heating.

However, such protection as a rule is insufficient, in particular inview of the considerable heat radiation below the inside of the dome. Inthe new air heater the said space is according to the inventionpreferably filled up at least in part with deformable refractorymaterial. Such material could be a refractory felt or the like.

The invention will now be explained in more detail with reference to theenclosed more or less diagrarnmatic drawings, by way of example only. Inthese drawings;

FIG. 1 shows a hot blast stove according to the invention in side viewand partly in vertical section;

FIG. 2 shows detail I] in FIG. 1 in vertical section at an enlargedscale;

FIGS. 3, 4 and 5 show the same detail in somewhat different embodiments.

Like parts are indicated by like reference numerals in the severaldrawings.

In FIG. 1 reference numeral 1 shows an outer jacket of the upper end ofthe vertical cylindrical body and dome of an air preheater, being theouter steel lining thereof. This air preheater is of the type with aninterior stack 21, but a structure according to the invention could aswell be applied to air preheaters with an exterior burner stack, suchstructures being usual and known as such. A wall 22 separates this stack21 from a space 23, filled with a pile of heat-absorbing refractorybricks not shown. In well-known manner this preheater has an inlet at 24for combustible gas and combustion air to a burner 25 in the lower endof stack 21, an outlet 26 for heated air and a duct connection 27 forintroducing cold air when on blast and for discharging combustion gaseswhen on gas. A grid 28 supports the said pile of bricks. The airpreheater moreover lms the usual slide valves at the inlets and outletsfor gases and air, which are familiar to the expert and thus not shown.

The vertical cylindrical body enclosed by jacket 1 is covered by a domeprotruding with its lower edge radially outside said jacket and engagingaround the top of the cylindrical masonry within said jacket. The outersteel jacket of said dome is indicated by 2. The lower end of jacket 2is divided by intermediary into zones or strips 3 which in a mannerwhich will be described below form part of the connection of dome jacket2 to cylindrical jacket I.

In contact with the inner wall ofthe steeljacket I of the vertical bodya refractory lining is present, indicated diagrammatically by partlyshown layers 4, 5 and 6. The refractory dome 7 proper is positioned atsome distance interiorly of the outer steel jacket 2 of the dome andextends downwardly past the upper edge of layers 4, 5 and 6 to a greaterradial distance from the axis of the heater. At a distance from andoutside dome 7a refractory heat insulating layer 8 of bricks is presentin contact with the outer steel jacket 2.

Each strip 3 constitutes part of an I-shaped beam having a web 9 and anopposite flange l0, and said beam is, at a considerable distance belowthe upper edge of layers 4, 5 and 6, welded to the steel outer jacket 1of the vertical body. In this zone the temperature of the jacket issubstantially lower than at the upper edge of the vertical body. lfthesteel outer jacket I in this zone is not sufficiently rigid, it ispossible to apply a suitable reinforcement in this zone, such as acontinuous surrounding steel annulus between the steel jacket 1 and theI-shaped beams. It is also possible to provide the web 9 at its lowerend with flanges extending transversely over the outside of the steeljacket and in contact therewith over a large area. Such an annulus orsuch flanges would have a vertical section in FIG. 2 as shown in adotted line and as indicated by 29.

Between the zone of the largest protrusion and radial extension of thedome jacket 2 and the upper end of the jacket 1 there is a connectingpart 11 being stepped in shape. Thanks to this stepped shape it ispossible for this connecting part to connect jacket parts 1 and 2 in agastight manner. On the central step of this stairs the refractory dome7 rests.

The upper end 12 of the brackets is also shaped in a stepwise manner.Between this upper edge 12 and part 11 there are sliding blocks 13, 14and 15, which may be secured or not to one of the faces in contacttherewith, so to the upper surface 12 of the brackets 9 or to the lowersurface of part 11. This makes it possible to take up any deformation ofpart 11 in a radial sense with respect to the brackets because thecontacting parts are easily allowed to slide with respect to each other.

FIG. 3 gives a simplified structure of the same detail as FIG. 2. inFIG. 3 the connecting wall 11 of the outer metal jacket as shown in FIG.2 is replaced by a conical element 16, onto which the dome '7 rests, andan elastic connecting part 17. The conical element 16 is rigidly securedto the upper side of the brackets. In this embodiment a movement in aradial sense of the dome 7 with respect to the upper surface of thebrackets is excluded. To this end the inner flange of the brackets iscontinued to extend upwardly a short distance past conical element 16,so that the lower edge of the dome 7 rests in a deepened recess, whichit cannot easily leave. The supporting forces between dome 7 and element16 are restricted to a force perpendicular to the surface of element 16thanks to the conical shape of this element and to the fact that dome 7in this part extends exactly perpendicularly to element 16.

ln FIG. 4 an alternative of the structure of FIG. 3 is shown in whichthe connecting part 18 of the metal jacket smoothly merges into both theupwardly extended part of the inner flange l0 and into the metaljacket 1. Thereby a higher elastic deformability is obtained.

FIG. 5 shows yet another alternative. This differs from the alternativeof FIG. 4 in that the metal jacket connecting part 19 is not positionedas an upward extension of the inner flange 10, but as an inwardextension of the conical element 16. This simplifies the structure as tothe method of making it. The arresting of the lower edge of dome 7against movement in a radial sense is in this structure obtained byapplying, e.g. by welding, two longitudinal circular ribs 20 all aroundon element 16. The lower bricks of dome 7 have recesses, so that theyfit over these ribs.

We claim:

1. A regenerative air heater such as a hot blast stove for a blastfurnace plant, comprising a preferably cylindrical hollow vertical bodyof refractory bricks closed at the top by a dome of refractory bricksoverlying and protruding radially outside said vertical body at the topthereof, the entire structure being surrounded by a jacket of steel ofthe vertical body and of the dome, characterized in that the dome isbuilt up on and is supported by a steel annular element which is in agas-tight manner connected to the outer steel jacket of the dome and ofthe vertical cylindrical body, the connection of the said annularelement to the steel jacket of the vertical body and/or of the domeextending with respect to $$$$$fililf lllisllin'fiflr element issupported by a row of brackets secured to the outer jacket of thevertical body at a larger distance downwards from the upper edge of thevertical body than where the connection of the annular element to thevertical body is positioned, and preferably at at least twice thelastmentioned distance.

2. An air heater according to claim 1, characterized in that the annularelement is rigidly secured to the brackets.

3. An air heater according to claim 1, characterized in that the annularelement is immediately rigidly connected to the outer jacket of thedome, so without intermediary parts, but is connected to the outerjacket of the vertical body by a connecting part which extendsalternately in different directions.

4. An air heater according to claim 3, characterized in that theconnecting part includes three curved parts which in total occupy anangle of 200 to 350.

5. An air heater according to claim 1, characterized in that the annularelement has the shape of a frustoconical body and that the lower edge ofthe dome is positioned perpendicularly to this element.

6. An air heater according to claim 1, characterized in that the annularelement is provided with means for arresting the position of the loweredge of the inner refractory brick dome against radial movement.

7. An air heater according to claim 1, characterized in that an outerflange of the brackets smoothly merges into the outer metal jacket ofthe dome.

8. An air heater according to claim 1, characterized in that the spacebetween the dome, the vertical body and the connecting part betweenannular element and outer jacket of the vertical body is at least inpart filled with deformable refractory material.

1. A regenerative air heater such as a hot blast stove for a blastfurnace plant, comprising a preferably cylindrical hollow vertical bodyof refractory bricks closed at the top by a dome of refractory bricksoverlying and protruding radially outside said vertical body at the topthereof, the entire structure being surrounded by a jacket of steel ofthe vertical body and of the dome, characterized in that the dome isbuilt up on and is supported by a steel annular element which is in agas-tight manner connected to the outer steel jacket of the dome and ofthe vertical cylindrical body, the connection of the said annularelement to the steel jacket of the vertical body and/or of the domeextending with respect to the axis of the vertical body alternately in amainly radial and in mainly axial directions and that this annularelement is supported by a row of brackets secured to the outer jacket ofthe vertical body at a larger distance downwards from the upper edge ofthe vertical body than where the connection of the annular element tothe vertical body is positioned, and preferably at at least twice thelastmentioned distance.
 2. An air heater according to claim 1,characterized in that the annular element is rigidly secured to thebrackets.
 3. An air heater according to claim 1, characterized in thatthe annular element is immediately rigidly connected to the outer jacketof the dome, so without intermediary parts, but is connected to theouter jacket of the vertical body by a connecting part which extendsalternately in different directions.
 4. An air heater according to claim3, characterized in that the connecting part includes three curved partswhich in total occupy an angle of 200* to 350* .
 5. An air heateraccording to claim 1, characterized in that the annular element has theshape of a frustoconical body and that the lower edge of the dome ispositioned perpendicularly to this element.
 6. An air heater accordingto claim 1, characterized in that the annular element is provided withmeans for arresting the position of the lower edge of the innerrefractory brick dome against radial movement.
 7. An air heateraccording to claim 1, characterized in that an outer flange of thebrackets smoothly merges into the outer metal jacket of the dome.
 8. Anair heater according to claim 1, characterized in that the space betweenthe dome, the vertical body and the connecting part between annularelement and outer jacket of the vertical body is at least in part filledwith deformable refractory material.